1. Field of the Invention
This invention relates generally to heat exchangers and more particularly, it relates to a wet tube-in-fin, flat-top evaporator coil of the type in which a stream of air to be cooled is forced across the finned surfaces in a vertical air flow.
2. Description of the Prior Art
In U.S. Pat. No. 2,046,968 issued to J. C. Raisley on July 7, 1936, there is shown a plurality of fins threaded on the tubes of a refrigerant coil. Each of the fins are formed with a series of indentations on both sides and are alternately arranged to form pockets adapted for the collection and retention of drops of condensed moisture.
In U.S. Pat. No. 2,099,665 issued to R. T. Smith on Nov. 16, 1937, there is shown a refrigerating coil with which is associated a series of substantially parallel fins mounted in vertical planes. The adjacent fins of the series are spaced apart at a given distance for effective drainage of water droplets.
In U.S. Pat. No. 3,223,153 issued to C. S. Simpelaar on Dec. 14, 1965, there is shown a heat exchanger structure wherein a sinuous continuous metal sheet having a parallel series of aligned slots are folded in order to produce adjacent pleats constituting the spaced fins.
In U.S. Pat. No. 3,759,050 issued to R. S. Slaasted et al. on Sept. 18, 1973, there is disclosed a method of cooling a gas and removing moisture therefrom which includes a plurality of spaced louvers on the fins immediately above the tubes for providing liquid flow paths of liquid condensate along the tubes onto the tubes and from there down the tubes.
In U.S. Pat. No. 3,902,551 issued to A. T. Lim et al. on Sept. 2, 1975, there is disclosed a plate fin type heat exchanger construction in which the fin members are formed with longitudinal corrugations for removing condensate droplets by gravity flow to a drain pan.
In U.S. Pat. No. 3,923,098 issued to R. A. Ares on Dec. 2, 1975, there is disclosed a heat exchanger having at least one condensate channel of a U-shaped configuration disposed in the downstream edge of each of the fins for collection and drainage of the condensate.
Heretofore, it has been generally known that condensate droplets accumulate on the underneath side of evaporator coils. As the droplets of water increases in size due to its unstable condition in a varying static pressure field, the large main drops of water will changes its shape to satisfy its equilibrium condition in which the main drops possess a bulged part. The bulged parts will disintegrate from the main drops causing a blow-off and are entrained for a distance by the vertical airstream flow into the conditioned air. This results in the undesired conditions of water droplets entrained into the duct system, excessive pressure drop through the evaporator coil and decreasing the heat transfer coefficient of the finned surfaces, thereby reducing significantly the capacity of the evaporator coils.
It would be, therefore, desirable to provide a means for controlling the blow-off of water droplets from the surface of the evaporator tubes by transforming the large unstable drops into a plurality of small droplets so as to increase its stability. Consequently, the critical face velocity at which blow-off occurs can be increased significantly. Since the capacity of the evaporator coils increase with face velocity, the heat transfer characteristic of the evaporator coils is also greatly improved in performance and yet without increasing the pressure drop. This improved operation is accomplished by providing a plurality of sheet-like fins having a series of openings for receiving the evaporator tubes and a number of tabs disposed vertically and directly below the openings for contacting the condensate hanging underneath the tubes.